1. Field of the Invention
The present invention relates generally to improvements in charge segments formed of explosive materials which are assembled together to form a pipe cutting or severing apparatus or to form a shaped charge for perforating a well bore. The invention also pertains to methods of making pelletized charge segments of pressed explosive materials and to a method for assembling such charge segments into a pipe cutting, severing or perforating device.
2. Description of the Prior Art
A variety of tubing and casing cutters are known in the prior art for severing pipe, tubing and casing in oil and gas wells in order to allow retrieval of the pipe. One common cutter design involves the use of shaped charge wafers which are comprised of pressed explosive material, a liner and a backup plate of some material, typically steel material. This assembly is placed within a housing and is lowered down the well in order to cut the pipe.
U.S. Pat. No. 4,354,433, issued Oct. 19, 1982, to Owen shows another type of cutter in which an annular shaped charge is contained within a carrier and which is used as a pipe cutting or severing apparatus. The charge is made up of eight or more charge segments disposed in side to side butting relationship. Each charge segment has a die formed metal band and a charge load. The pipe cutting apparatus has the general configuration of a short cylinder or disk provided with a circumferential slot. The cutter is typically suspended within a pipe to be cut, in which case the charge segments are disposed to face radially outward.
The above described device to Owen thus uses xe2x80x9csegmentsxe2x80x9d that are assembled together in a housing, creating a system equivalent of the wafer type cutter in terms of explosive charge. The segmented cutter had certain advantages over the prior art in the manufacture of pipe cutting devices. In the prior art Owen cutter, the explosive segments were pressed and formed in one operation and then modified to fit the desired configuration of the cutter. This operation was all carried out at the manufacturing facility.
In the case of shaped charges which are used in well perforating operations, such charges are manufactured by pressing an explosive material between a cup-shaped case or container or a shaped charge liner. This operation can be done in a single stage or in multiple stages, but in all cases the explosive, case and liner are unitized at the manufacturing facility prior to shipment.
The present invention has as its object to provide an improved charge segment and assembly for cutting, severing or perforating pipe, casing and tubing, particularly pipe used in a well bore.
In the present method of manufacturing a well tubing and casing cutter, an explosive powder material is pressed to form a free standing segmented pellet having a desired shape and multiple faces. A liner is adhered to at least one face of the segmented pellet. A plurality of the pressed pellets are arranged in a circular pattern on a backup plate and are adhered to the backup plate to form a charge assembly. An ignition source is provided for the charge assembly with a plurality of the assemblies being stacked one upon the other within a container to form a well tubing and casing cutter.
The pressed pellets can be assembled on the backup plate at a location remote from the manufacturing facility where the pellets were pressed. Preferably, the tubing and casing cutter includes a central pelletized disk of explosive material with the plurality of pressed segmented pellets being arranged in a circular pattern about the pelletized disk on the backup plate. The disk and segmented pellets are adhered to the backup plate with a suitable glue or adhesive, each segmented pellet also having a liner adhered to at least one face thereof. The preferred glue used for securing the liner to the segmented pellets and for adhering the pellets and central disk to the backup plate is a silicone adhesive containing powdered copper.
A method for manufacturing a shaped charge is also shown. In this case, a plurality of segmented pellets are formed of a free standing pressed explosive powder material. The segmented pellets are arranged within a cup-shaped container. The assembly can be performed at a location remote from the manufacturing facility at which the pellets were pressed. The cup-shaped container has an interior for receiving the pellets and a mouth opening. The pressed segmented pellets are selectively sized to form a body which tapers inwardly toward the mouth opening of the cup-shaped body when the pellets are stacked one atop another. A V-shaped liner is positioned within the mouth opening of the container atop the stacked pressed pellets to complete the assembly.
Additional objects, features and advantages will be apparent in the written description which follows.